1. Field of the Invention
The present invention relates to a plating method in which a cup-type plating apparatus is used for plating semiconductor wafers.
2. Earlier Technologies
Cup-type plating methods have been known as a method for conducting bump plating on semiconductor wafers (see Japanese Utility Model Application Laid-open No. 122067/1991 and Japanese Patent Application Laid-open No. 320978/1994). In the cup-type plating methods, a plating process is conducted by the steps including: placing a wafer on a support provided along an upper portion of an opening of a plating tank; supplying plating solution by flowing the solution upward through a bottom of the plating tank; and bringing the plating solution into contact with a surface to be plated of the wafer. The cup-type plating methods can provide identical plating continuously by replacing wafers being placed on the support, thus have been widely used as suitable methods for automation of plating processes and small lot production.
However in the cup-type plating methods, replacement of wafers on each occasion of plating process often causes adhesion of plating solution, after a plated wafer is detached, on the support on which the wafer was placed. On this condition, when another or new wafer is placed, the periphery of the wafer will inevitably come in contact with the plating solution adhered on the support.
Such a phenomenon has been a mal-factor that inhibits satisfactory plating in the cup-type plating methods. Especially, when wafers with seed metal, that is wafers which are preliminarily covered at a surface to be plated thereof with metal such as Cu are plated, the plating solution adhered on the support causes conditions not preferable to a plating process. Specifically speaking, after a wafer with seed metals is replaced with another but before placed on the support to be supplied with plating current, the plating solution adhered on the support will dissolve the seed metal at the periphery of the wafer placed. The wafer with seed metal supplies a surface to be plated with plating current via the seed metal, and if the seed metal on the periphery of the wafer is dissolved, plating current may not be uniformly supplied.